High Volumes of Resistance Exercise Are Not Required for Greater Bone Mineral Density during Growth CAMMIE P. AHLES 1 , HARPREET SINGH 1 , WOOJIN JOO 1 , YVONNE LEE 1 , LUCY C. LEE 1 , WILLIAM COLAZAS 1 , R. ANDER PIERCE 1 , ANURADHA PRAKASH 1 , S. VICTORIA JAQUE 2 , and KEN D. SUMIDA 1 1 Schmid College of Science & Technology, Chapman University, Orange, CA; and 2 Department of Kinesiology, California State University, Northridge, CA ABSTRACT AHLES, C. P., H. SINGH, W. JOO, Y. LEE, L. C. LEE, W. COLAZAS, R. A. PIERCE, A. PRAKASH, S. V. JAQUE, and K. D. SUMIDA. High Volumes of Resistance Exercise Are Not Required for Greater Bone Mineral Density during Growth. Med. Sci. Sports Exerc., Vol. 45, No. 1, pp. 36–42, 2013. Purpose: The purpose of this study was to determine the minimum amount of resistance exercise that would stimulate bone formation, via an elevation in bone mineral density (BMD), during the growth period in male rats. Methods: Forty male rats were randomly divided into control group (Con, n = 8), one ladder climb resistance-trained group (1LC, n = 8), two ladder climb resistance-trained group (2LC, n = 8), three ladder climb resistance-trained group (3LC, n = 8), and four ladder climb resistance-trained group (4LC, n = 8). All exercised groups were conditioned to climb a vertical ladder with weights appended to their tail 3 dIwk j1 for a total of 6 wk. Results: After 6 wk, left tibia BMD (mean T SE) was significantly greater for 2LC, 3LC, and 4LC (0.233 T 0.003 gIcm j2 ) when compared with Con (0.218 T 0.003 gIcm j2 ). Left femur BMD was significantly greater for 2LC, 3LC, and 4LC (0.318 T 0.003 gIcm j2 ) when compared with 1LC (0.299 T 0.008 gIcm j2 ) and Con (0.289 T 0.010 gIcm j2 ).There were no significant differences in BMD between 2LC, 3LC, and 4LC groups. Conclusion: The results suggest that during growth, a low amount of resistance exercise was just as effective as high volumes of strength training for stimulating bone modeling. Key Words: TIBIA, FEMUR, DXA, THREE-POINT BENDING TEST A n elevation in peak bone mass has been advocated as a prophylactic against osteoporosis (10,30). Given that the hormonal milieu associated with the maturation process stimulates bone modeling, the growth period would be an optimal time to promote an even greater increase in peak bone mass. In support, exercise intervention studies in children appear to be more effective for bone formation compared with the elderly where the impact of exercise helps to prevent and/or to minimize bone loss (26). Elevating peak bone mass can be accomplished with resis- tance exercise that has been promoted as an effective method to stimulate bone formation (12,26). Thus, incorporating resistance exercise during the growth period would be ben- eficial in maximizing peak bone mass with the potential to attenuate the bone loss associated with advanced age. However, the amount of resistance exercise to implement during the growth period for maximal stimulation of bone accrual remains to be determined. Turner and Robling (27) first described an exercise pro- tocol with the potential to augment bone formation via interrupted exercise bouts throughout a training day rather than continuous exercise performed in a single training bout. Specifically, partitioning the exercise into multiple bouts allows the ‘‘mechanosensors’’ to reset and become restimu- lated, resulting in an even greater bone formation response (27). However, these initial studies were performed in anesthetized adult rats using a bone loading protocol for 16 wk (27). In a previous study, we sought to test this hy- pothesis by providing an additional stimulus for bone for- mation via interrupted resistance training during the growth period in conscious rats. We first attempted three bouts of exercise separated by 4 h (6), then two bouts of exercise separated by 12 h (5), and finally a single bout separated by 24 h (11). Given the relatively short training duration (i.e., 6 wk) and high volume of work performed, we chose to lengthen the time between each interrupted exercise bout to assist in the recovery of the mechanosensors. In all these previous studies, the total volume of work was equivalent between the interrupted and the continuous bouts of exercise (5,6,11). Despite our previous attempts to further augment bone formation (5,6,11), we found that the interrupted bouts Address for correspondence: Ken D. Sumida, Ph.D., Crean School of Health & Life Science, Chapman University, One University Drive, Orange, CA 92866; E-mail: sumida@chapman.edu. Submitted for publication April 2012. Accepted for publication July 2012. 0195-9131/13/4501-0036/0 MEDICINE & SCIENCE IN SPORTS & EXERCISE Ò Copyright Ó 2012 by the American College of Sports Medicine DOI: 10.1249/MSS.0b013e31826a5710 36 BASIC SCIENCES Copyright © 2012 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.